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I disagree. It is a useful perspective because it flies in the face of one's intuited perspective. How many of us would have estimated that the volume of water

I disagree. It is a useful perspective because it flies in the face of one's intuited perspective. How many of us would have estimated that the volume of water would be so small? We visualize the oceans as really deep gouges on the Earth's surface because to our puny asses a depth of 1 to 8 miles sounds amazingly deep. We'd never guess that even with miles deep depressions and miles high mountains, the Earth is smoother than a billiard ball: http://blogs.discovermagazine.com/badastronomy/2008/09/08/ten-things-you-dont-know-about-the-earth/ http://blogs.discovermagazine.com/badastronomy/2008/09/08/te... Combining both of these counter-intuitive perspectives tells us that our oceans are akin to a very thin film of water on a wet billiard ball. A thin dirty film is all that billions of bacteria needs to thrive on a billiard ball, and a thin dirty film is all that billions of animals and plants need to thrive on Earth.

b_emery 15y ago
> a very thin film of water on a wet billiard ball You're right. The average depth of the ocean is about 4km, while the earth's radius is about 6371km.
_delirium 15y ago
> How many of us would have estimated that the volume of water would be so small? Well, I did, but that's because it's already been emphasized to me before (in some kind of geology class) how little volume the crust+troposphere shell takes up. It's not a water-specific thing, but a crust/troposphere thing, of which water is a subset. And actually I think the real underlying counterintuition is just a geometric one, that people don't realize little volume spherical shells occupy relative to solid spheres.
deleted 15y ago
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Someone 15y ago
"How many of us would have estimated that the volume of water would be so small?" I did. Before reading the article, I did the following very rough calculation in my head: earth is 40,000 km (equator length) by 20,0000 km (pole to pole). An average water depth of 1 km gives 800M cubic kilometers of water. From there, I guesstimated the diameter at about 1000km (a 1000km cube would be 1000M cubic kilometers). It might have ended up smaller if I hadn't approximated the surface of the earth to be a cylinder, but who cares about such a 'puny' rounding error, given that I totally guessed at that 1 km?

b_emery 15y ago

> a very thin film of water on a wet billiard ball You're right. The average depth of the ocean is about 4km, while the earth's radius is about 6371km.

_delirium 15y ago

> How many of us would have estimated that the volume of water would be so small? Well, I did, but that's because it's already been emphasized to me before (in some kind of geology class) how little volume the crust+troposphere shell takes up. It's not a water-specific thing, but a crust/troposphere thing, of which water is a subset. And actually I think the real underlying counterintuition is just a geometric one, that people don't realize little volume spherical shells occupy relative to solid spheres.

deleted 15y ago

[deleted]

Someone 15y ago

"How many of us would have estimated that the volume of water would be so small?" I did. Before reading the article, I did the following very rough calculation in my head: earth is 40,000 km (equator length) by 20,0000 km (pole to pole). An average water depth of 1 km gives 800M cubic kilometers of water. From there, I guesstimated the diameter at about 1000km (a 1000km cube would be 1000M cubic kilometers). It might have ended up smaller if I hadn't approximated the surface of the earth to be a cylinder, but who cares about such a 'puny' rounding error, given that I totally guessed at that 1 km?